1. Field of the Invention
This invention relates to a method of purification of sulfur dioxide containing process gas streams resulting from the combustion of sulfur containing compounds. More particularly, this invention relates to such a method wherein purification is carried out in a single step.
2. The Prior Art
Numerous procedures have been developed for the production of sulfuric acid, all of which involve catalytic oxidation of sulfur dioxide to sulfur trioxide in the presence of some catalyst and absorption of the sulfur trioxide into concentrated sulfuric acid to form further sulfuric acid. Sulfur dioxide employed in the catalytic oxidation is usually formed by the combustion of a sulfur containing feed stream. The sulfur containing feed stream can be waste sulfuric acid, elemental sulfur, hydrogen sulfide, pyrites or other sulfides, or sludge acid derived from petroleum refining or any other compatible sulfur containing materials. In addition to sulfur dioxide, water vapor and oxygen, the combustion process stream includes carbon dioxide and minor quantities of solid materials. Prior to using the process gas stream in the catalytic oxidation reaction, the stream must be cooled and both the solid materials and the water must be removed.
Several methods have been proposed for cooling the hot combustion process gases, and for removing water and solid contaminants. Most of these processes employ multistep procedures. For example, processes in which the sulfur dioxide containing process gas stream in a sulfuric acid process is scrubbed with concentrated sulfuric acid to remove water vapor prior to catalytic oxidation of the sulfur dioxide to sulfur trioxide are described in U.S. Pat. Nos. 940,595; 2,019,893; 2,028,733; 2,038,429 and 2,174,739. Another prior art patent, U.S. Pat. No. 3,475,120, describes a procedure in which the gas is first cooled by passing through a heat exchanger and is then scrubbed with water to remove entrained solid particles and also for gas cooling purposes. The cooled/scrubbed gas which now contains sulfuric acid aerosol mist is passed through some type of electrostatic precipitator, or other type of mist eliminator to remove the acidic aerosol mist. The process gas stream which is now free of entrained liquid droplets does include water vapor which must be removed prior to catalytic oxidation of the sulfur dioxide component to sulfur trioxide. To remove the water vapor, the process gas stream is scrubbed with concentrated sulfuric acid having a strength in the range of from 78% to 100% sulfuric acid content by weight. The concentrated sulfuric acid acts as a dehydrating agent and readily absorbs all of the water vapor from the process gas stream.
These multistep prior art purification procedures suffer from a number of inherent disadvantages. For example, these procedures are time consumming, require large capital expenditures and have large manpower and maintenance requirements.